linux-kernel - Re: Multicast: handling of STA disconnect

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Message-ID: <CAE2MWkn=ygeVwj=j7ggLd+10mGjPJEC8Et5MGHVzs=dGWLccYg@mail.gmail.com>
Date:   Mon, 20 Mar 2023 23:11:19 +0530
From:   Ujjal Roy <royujjal@...il.com>
To:     Nikolay Aleksandrov <razor@...ckwall.org>
Cc:     roopa@...dia.com, netdev@...r.kernel.org,
        Kernel <linux-kernel@...r.kernel.org>,
        bridge@...ts.linux-foundation.org
Subject: Re: Multicast: handling of STA disconnect

Hi Nik,

Any idea if the station connects back immediately after say 10 sec?
How to resume the session immediately if we delete the MDB on
disconnect? Currently, the station needs to wait until the next
general query to come to STA.

My idea is to send a general query to that specific port to resume the
session immediately from the STA connect event. This will create the
MDB immediately and resume the stream, as we have deleted the MDB from
disconnect.

Thanks,
UjjaL Roy

On Mon, Mar 20, 2023 at 10:55 PM Ujjal Roy <royujjal@...il.com> wrote:
>
> Hi Nik,
>
> Flushing MDB can only be done when we are managing it per station not
> per port. For that we need to have MCAST_TO_UCAST, EHT and FAST_LEAVE.
>
> Here one more point is - some vendors may offload MCAST_TO_UCAST
> conversion in their own FW to reduce CPU.
>
> So, the best way is to have MCAST_TO_UCAST enabled and MDB will become
> per station, so we can delete MDB on disconnect. Shall, I create one
> patch for review?
>
> Thanks,
> UjjaL Roy
>
> On Mon, Mar 20, 2023 at 5:38 PM Nikolay Aleksandrov <razor@...ckwall.org> wrote:
> >
> > On 20/03/2023 13:45, Ujjal Roy wrote:
> > > Hi Nikolay,
> > >
> > > I have some query on multicast. When streams running on an STA and STA
> > > disconnected due to some reason. So, until the MDB is timed out the
> > > stream will be forwarded to the port and in turn to the driver and
> > > dropps there as no such STA.
> > >
> > > So, is the multicast_eht handling this scenario to take any action
> > > immediately? If not, can we do this to take quick action to reduce
> > > overhead of memory and driver?
> > >
> > > I have an idea on this. Can we mark this port group (MDB entry) as
> > > INACTIVE from the WiFi disconnect event and skip forwarding the stream
> > > to this port in br_multicast_flood by applying the check? I can share
> > > the patch on this.
> > >
> > > Thanks,
> > > UjjaL Roy
> >
> > Hi,
> > Fast leave and EHT (as that's v3's fast leave version) are about quickly converging when
> > a leave is received (e.g. when there are no listeners to quickly remove the mdb). They
> > don't deal with interface states (IIUC). Why don't you just flush the port's mdb entries
> > on disconnect? That would stop fwding.
> >
> > Cheers,
> >  Nik
> >
> >